There is a bug in the c# example code of the transaction section:

https://docs.mongodb.com/master/core/transactions/?_ga=2.203887700.515816747.1531800617-1973885362.1531800617#retry-transaction-and-commit-operation

The example source code is at:

https://github.com/mongodb/mongo-csharp-driver/blob/master/tests/MongoDB.Driver.Examples/TransactionExamplesForDocs/RetryExample3.cs

At line 88 and line 91, when we're doing the update and insert operations, we should pass `session` as the first parameter, in order to put them in the transaction and demonstrate how the transaction works. And that is the purpose of this example.